Abstract: An induction motor drive having source and load side converters with individual control channels for the respective converters includes a cross tie arrangement between the channels for increased system stability.

Abstract: An induction motor drive including a current source inverter system having controlled turn on and turn off semiconductors in a load side inverter selectively places notches in the waveshape of the current supplied to the parallel combination of the motor and a capacitor bank for the minimization of harmonics.

Abstract: A power conditioner having a source and load converter each using a phase-locked loop to control their respective converter firings achieves synchronization with a supply mains by determining the phase error between supply mains and motor voltages by obtaining the instantaneous difference between the output signals of the source and load phase locked loops. This phase error is passed through a simple gain and summed with a speed regulator setpoint, which now becomes an inverter frequency regulator with the nominal setpoint being the supply mains frequency. The voltage amplitude error between the supply mains and the motor is obtained by comparing the absolute value of the source voltage with the properly scaled absolute value of the integrated motor voltage and this error signal is input to the flux regulator in a synchronous or induction motor controller in place of the normal input when not synchronizing.

Abstract: A single microcomputer controls the firing time determination for two independent current regulators for two six pulse AC/DC converters which are part of a twelve pulse parallel controlled current inverter (CCI) AC motor drive. A very short high priority interrupt occurs when a motor channel source converter thyristor fires. This interrupt calls a longer, low priority current regulator interrupt informing it that a master channel source converter thyristor has just been fired. The current regulator causes a count to be loaded into a master fire counter and also loads a firing mask into a hardware latch or buffer. When the master fire counter times out the next thyristor pair of the master channel source converter is fired directly out of hardware. Similarly, there is a separate slave channel fire counter loaded after the current regulator is called by a short high priority interrupt when a thyristor in the slave channel source converter fires.

Abstract: A controlled current inverter (CCI) induction motor drive is controlled by controlling motor current and the angle between motor flux and motor current. The angle between motor flux and current is derived directly via a microcomputer phase-locked loop synchronized to the integrated motor voltage. The delay between the application of a firing signal to a thyristor and the initiation of line current is determined and compensated for to achieve the desired angle between motor flux and motor current.

Abstract: A method of starting an AC motor from any initial speed using open loop control is provided. Sufficient current is provided to the motor so that motor flux can be developed. The frequency provided to the AC motor is varied and the stator frequency at which the motor peak flux occurs is determined. A transition to a control responsive to an external command at approximately the stator frequency at which the peak flux occurred is made.

Abstract: A microprocessor based pulse-width modulated variable speed drive control system providing optimal switching angles based on minimizing r.m.s. current ripple. In addition, a closed loop double deadband control interacts with the optimal switching angles to insure close following of a desired function of a specified variable to be controlled.

Abstract: A fault protective system for a load commutated inverter motor drive including an AC to DC source side converter coupled from an AC source to a DC to AC load side converter via a DC link circuit and wherein the load side converter supplies AC power of varying magnitude and frequency to the synchronous motor load. A pair of microcomputers interlinked by a common digital memory respectively control the inverters and interface with hardware type sensor means for detecting the occurrence of a plurality of different types of faults. Additionally, a number of stored instructional sets or programs are respectively included in both microcomputers to detect by software means another plurality of faults. The detection of a fault on either side of the link circuit is communicated to the respective computer which subsequently communicates with the other microcomputer to effect a coordinated protective action in response to thyristor cell failures, circuit failures, and abnormal operating conditions.

Abstract: A load commutated inverter synchronous motor drive system wherein a thyristor firing control of the inverter is determined by the amplitude of pesudo flux waveforms which are derived from the integral of the line voltages coupling the inverter to the motor being driven. A firing strategy is provided based on the premise that optimum thyristor firing in a load commutated inverter operating at a leading power factor occurs at a point just below the peak of the forthcoming pseudo flux waveform which point comprises an amount of volt-seconds necessary to effect current commutation plus a nominal safety margin. The determination and control is implemented, preferably, in a software phase lock loop but can, when desirable, be implemented in hardware.

Abstract: The load side converter or inverter in a load commutated inverter motor drive, including a source side AC to DC converter coupled to a DC to AC converter via a DC link circuit, is adapted to have at least three and preferably four modes of operation for bringing an AC motor load, and more particularly a synchronous motor, up to speed. In the preferred embodiment, the first mode constitutes an idle mode wherein the converter thyristors are maintained in a non-conducting state until commanded for normal operation. The second mode constitutes an initial start-up mode which assumes no knowledge of initial rotor position of the motor and simply utilizes a fixed low frequency firing signal to sequentially gate the thyristors using forced commutation to commutate the off-going thyristor.

Abstract: A control system for powering an AC load such as a polyphase synchronous motor having at least two sets of three phase (3.phi.) windings. Each three phase winding set is powered by an independently operable six pulse load commutated inverter drive including a source side converter and a load side converter coupled together by means of a DC link and wherein the source side converter and the load side converter are operated in accordance with respective current and load angle regulators which respond to torque command signals generated by speed regulators.

Abstract: The effect of commutation notches 35 appearing in the nominally sinusoidal alternating current (AC) line-to-line voltage, for example, v.sub.ab used to synchronize the firing of thyristors in three phase, phase-locked power converters 12 and 14 is essentially eliminated by reconstructing the corrupted line-to-line voltage by summing the integral of the corrupted line-to-line voltage .PSI..sub.ab with a signal proportional to the product of the delta load current, for example, i.sub.ab and the commutation inductance L.sub.c. The composite waveform .PSI..sub.ab +i.sub.ab .times.L.sub.c) resulting from the summation has well defined zero crossings 41 from which synchronizing pulses are generated for synchronizing the phase-locked thyristor firing circuit 18 implemented by either software or hardware techniques. Additionally, the reconstructed waveform is used to control commutation, particularly in the control of a load side converter i.e. inverter 14 which is utilized in an AC motor drive system.

Abstract: A microprocessor based pulse-width modulated variable speed drive control system providing optimal switching angles based on minimizing r.m.s. current ripple. In addition, a closed loop double deadband control interacts with the optimal switching angles to insure close following of a desired function of a specified variable to be controlled.

Abstract: A plurality of arbitrarily loaded induction machines are operated from a single, controlled current inverter by regulating the amplitude of inverter output current in response to the average of the individual induction machine phase angles, the machine phase angle being the phase relationship magnitude between machine air gap flux and current, and by regulating the frequency of inverter output current in response to the average of the individual induction machine phase angle and the slip frequency of the most heavily loaded induction machine. The most heavily loaded induction machine is thus assured of having sufficient flux, thereby greatly reducing the possibility of machine pull-out and resultant inverter instability.

Abstract: A controlled current inverter motor control system including a controlled source of direct current for supplying a variable frequency inverter by way of a direct current link circuit which includes, within the link circuit, a selectively insertable dynamic braking resistive element. Upon a call for a dynamic braking mode of operation, the source of direct current is short circuited and the normal operational or running control of the motor is discontinued. Special circuitry is provided which then forces a special frequency control of the inverter to thus control the angle between the motor flux and motor current to a prescribed value proportional to the extant value of a motor operating parameter (motor current or motor flux) prior to the insertion of the dynamic braking resistive element into the link circuit.

Abstract: Closed loop control of a pulse width modulated inverter-induction machine drive system is accomplished with a pair of microcomputers. The first microcomputer generates a periodic interrupt signal and a reference signal representative of the desired magnitude of a preselected induction machine parameter, the reference signal varying in frequency and amplitude in accordance with an externally-varied frequency value and amplitude value, respectively. The second microcomputer, when interrupted by the first microcomputer, computes the difference between the first microcomputer reference signal magnitude and the actual preselected machine parameter magnitude and the difference between the actual inverter output current magnitude and a preset limit, and controls inverter thyristor conduction accordingly.

Abstract: A controlled current inverter system forms the basis of an a.c. motor drive system for furnishing the motor load with a variable frequency, variable magnitude a.c. current from an inverter which is supplied from a variable d.c. current source by way of a d.c. link including an inductor. Torque is the control parameter employed in the system and the motor speed and torque are controlled through the control of motor flux and motor current, by maintaining a controlled ratio between the direct and quadrature motor currents, through separate control paths to the d.c. source and the inverter. A third control path functioning on the difference between the desired and actual motor flux serves as a modifier to the main control paths to improve overall operation and control. Means associated with the basic control paths provide for dynamic braking of the motor.

Abstract: A variable speed ac motor drive such as a controlled current inverter drive with load angle control generates an inverter frequency command signal which at low speed has a large ripple component and a small dc component representing the desired frequency. A variable frequency oscillator is responsive only to the dc component and supplies timing pulses to a ring counter which generates thyristor gating signals in the forward and reverse phase sequence. Smooth reversing over a wide range of torque is realized, and multipulse operation is inherent at low speeds to modulate the inverter output and minimize cogging torque.

Abstract: A digital firing control circuit is disclosed for controlling the generation of firing pulses for the eight controlled rectifiers (thyristors) in a bridge power converter in five distinct operating modes as well as effecting a smooth continuous transition between modes. The circuit compares and combines a plurality of locally generated time related waveforms according to a predetermined control algorithm in response to an applied analog command voltage to control the d.c. output voltage as well as providing certain protection functions such as end stops or inversion limits. The locally generated time related waveforms comprise sets of square voltage signals generated in accordance with selected cross-overs of the line voltages of the a.c. sources as well as the cross-overs of six firing reference ramp voltage signals separated from each other by 60.degree. and extending 240 electrical degrees.

Abstract: Variable frequency sine waves are converted to constant amplitude cosine waves using the relationship cos .omega.t = .sqroot.1-sin.sup.2 .omega.t. The converter has an almost instantaneous response characteristic and is suitable for a wide frequency range. An application is cosine timing waves for phase controlled converters and cycloconverters.